1. Priority Claim
This application claims the benefit of priority from Korean Patent Application No. 036091/2005, filed Apr. 29, 2005.
2. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of preventing distortion of a common voltage.
3. Description of the Related Art
Some liquid crystal display devices (LCDs) display an image by controlling optical transmittance of liquid crystal cells according to video signals. Some LCDs may be active matrix LCDs. The active matrix LCD includes a plurality of pixels in which switching elements are arranged in a matrix. Thin film transistors (TFTs) are used as the switching elements.
FIG. 1 is a schematic view of a related art LCD. In FIG. 1, the related art LCD includes a liquid crystal panel 2, a gate driver 4 and a data driver 6 for driving the liquid crystal panel 2, a timing controller 8 for controlling the gate driver 4 and the data driver 6, and a common voltage generator 10 for supplying a common voltage Vcom to the liquid crystal panel 2.
The liquid crystal panel 2 includes a plurality of gate lines GL1 to GLn, a plurality of data lines DL1 to DLm, and pixel regions defined by intersections of the gate lines GL1 to GLn and the data lines DL1 to DLm. TFTs and pixel electrodes are arranged in the pixel regions.
The gate driver 4 sequentially supplies scan signals to the gate lines GL1 to GLn in response to gate control signals outputted from the timing controller 8. The data driver 6 supplies 1-line data signals to the data lines DL1 to DLm at horizontal periods (H1, H2, . . . ) in response to data control signals outputted from the timing controller 8. The timing controller 8 generates the gate control signals for controlling the gate driver 4 and the data control signals for controlling the data driver 6.
Using a power supply voltage (Vdd) generated from a DC/DC converter (not shown), the common voltage generator 10 generates the common voltage Vcom for driving the liquid crystal panel 2. The common voltage Vcom is supplied to the common voltage supply line VL on the liquid crystal panel 2.
A predetermined electric field is generated by the common voltage Vcom and the data signals supplied to the data lines DL1 to DLm. Due to this electric field, the liquid crystals are displaced and display an image.
The common voltage supply line VL is formed on the same layer as the gate line. A gate insulating layer is formed on the common voltage supply line VL and the data line is formed on the gate insulating layer. Accordingly, the gate insulating layer is interposed between the data line and the common voltage supply line VL. Due to the gate insulating layer, a parasitic capacitor may be formed between the common voltage supply line VL and the data line.
The common voltage supply line VL is positioned in parallel to the data lines along an edge portion of the liquid crystal panel 2. Also, the common voltage supply line VL is positioned close to the gate lines in parallel.
Due to the parasitic capacitor, if data signal values between the data lines are rapidly changed, ripples are generated in the common voltage, Vcom, supplied to the common voltage supply line VL. If the common voltage Vcom is distorted due to the ripples supplied to the liquid crystal panel 2, a crosstalk phenomenon is caused. In some LCDs, to eliminate the crosstalk phenomenon, a common voltage compensator 12 may be provided.
The common voltage compensator 12 compensates for the distorted common voltage Vcom and supplies the compensated common voltage to the liquid crystal panel 2. The common voltage compensator 12 is configured with an operational amplifier (e.g., an OP-Amp). The common voltage Vcom distorted by the parasitic capacitor during one frame may be compensated during a next frame. Consequently, the distortion of the common voltage is prevented and thus an image quality is enhanced.
Although the common voltage Vcom is partially compensated by the common voltage compensator 12, the common voltage is still distorted in an entire region of the liquid crystal panel 2 since the common voltage supply line (VL) has a line resistance. If the compensated common voltage is supplied to an upper portion of the liquid crystal panel 2, the compensated common voltage is not distorted in the upper portion. However, the common voltage is distorted more severely toward the middle or lower portion of the liquid crystal panel 2. Of course, the upper portion of the liquid crystal panel 2 far from the supply point of the common voltage may still be distorted. Thus, even though the compensated common voltage is supplied to the liquid crystal panel 2, a shutdown crosstalk is generated from the upper portion to the lower portion of the liquid crystal panel 2. This shutdown crosstalk is still severely problematic.